As the computer processing increases in its speed and capacity, the amount of data also increases, and data conversion and data correction are also more frequently used. For example, a scanning correction corrects or repairs RGB data of an original document that is scanned by a scanner. The scanning correction includes CCD between-line correction, a main scanning register adjustment, shading correction, dot correction, vertical stripe correction and γ correction. Another example is an area separation where an edge or inside of binary lines and characters are determined. The area separation also separates dot image such as photographs. Lastly, the area separation separates chromatic elements from achromatic elements. Yet another example is for converting the corrected RGB data into a mapped data set such as CMYK image data and includes intermediate processes such as filtering, background removal, color mapping such as mapping to CMYK image data, color removal, main scanning sizing, main scanning shift, main scanning mirroring, sub scanning sampling, masking and digitization for monochromatic output. Another example is output correction for correcting the processed CMYK image data to match the printer output characteristics. The output correction includes printer γ correction and gradation process. The gradation process includes various processes such as intensity conversion, dithering and error diffusion.
The data processing includes sum of product for filtering, pattern matching for area separations, data conversion based upon a look up table (LUT) such as γ conversion and correction such as shading correction. When a preceding image data process and a proceeding image data process differ in a processing speed, it is necessary to temporarily store the data in a buffer. For filtering and pattern matching processes, since it is necessary to concurrently refer to multiple lines of pixel matrix of image data, the line buffer memory should have a capacity for a number of lines. For this reason, a buffer memory is generally used in image processing.
Japanese Patent Publication Hei 8-305329 discloses a signal process device in which an input data selector is sequentially connected to an input data latch, a memory unit, an output data latch and an output data select according to data flow. Furthermore, the device further includes a write address selector, a read address selector and a central processing unit (CPU) for controlling the selectors. The CPU selects a selector that specifies the memory for use as line memory for receiving TV image reception signal or for use as a look-up table for non-linear calculation. The CPU writes data for the look-up table in the memory unit.
As described above, for color image processing and adjustments, there are numerous data conversions and data corrections. For each of these processes, a necessary memory capacity and data processed amount often differ based upon a kind of data processing and data content. When a single memory resource accommodates the total memory need for the various processes, since memory is multiplexed depending upon the desired timing for the use of the memory in a sequential process flow, it is important to utilize the limited memory resource in an efficient manner. For color image processing, since the data amount is larger than that of chromatic image processing, the processing speed is essential. For this reason, the control of the memory resource is also an important issue. For example, in image formation devices such as a digital copier and a multifunctional machine, even if a processor is dedicated to various images processing, since the color image generally requires certain color specific processes and increases the amount of process data, the processing speed is reduced. In particular, in color image reading devices such as color scanners and color image forming devices such as color printers, the processing capacity for a color γ correction is a significant issue. For example, for the conversion of the RGB image data, at least three look-up tables are needed for each of the RGB data elements. Similarly, for the γ conversion of the YMCK image data, at least four look-up tables are needed for each of the YMCK data elements. The γ conversion takes time for the use of these look-up tables.
The data processing by the signal processing device as disclosed in Japanese Patent Publication Hei 8-305329 includes the line data insertion by the selection control from the output data selector as specified by the CPU during the line memory utilization mode and the data conversion based upon a look-up table during the look-up table utilization mode. It remains desirable to apply the disclosed signal processing device in order to speed up the above data conversion. A first objective of the current invention is to utilize the buffer memory in an efficient manner. A second objective is to implement the high-speed color data processing in a color image processing device.